/*
 * 谐均值计算（4分）
 */

#include <stdio.h>

double Calculate(double x, double y) {
	return 1 / ((1 / x + 1 / y) / 2);
}

int main() {
	setbuf(stdout, NULL);

	double x, y;

	printf("Input two doubles:\n");
	scanf("%lf%lf", &x, &y);

	printf("1/((1/x+1/y)/2) = %0.3f\n", Calculate(x, y));

	return 0;
}
